A flash interface for processing datasets

ABSTRACT

Systems and methods for managing content in a flash memory. Content or data in a flash memory is overwritten when the write operation only requires bits to be set. This improves performance of the flash and extends the life of the flash memory.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of U.S. patent applicationSer. No. 15/196,110 filed Jun. 29, 2016 and scheduled to issue Jul. 31,2018 as U.S. Pat. No. 10,037,164 which is hereby incorporated byreference in its entirety.

FIELD OF THE INVENTION

Embodiments of the invention relate to systems and methods forprocessing large datasets. More particularly, embodiments of theinvention relate to systems and methods for interfacing and interactingwith a memory device such as a flash memory device.

BACKGROUND

As the amount of data in computing systems continues to increase, thereis a strong desire for improvements that allows the datasets to beefficiently processed. DRAM (Dynamic Random Access Memory) and the likeare often too small to efficiently process large data sets. Algorithmsthat process the data out-of-core (using Hard Disk Drives (HDDs) tend tobe slow.

One potential solution is to introduce flash memory into the computingsystems. Flash memory is faster than HDDs and has the capacity toaccelerate dataset analysis. Even though flash memory can improve theprocessing capability of computing systems, flash memory has severalproblems that impact performance.

For example, conventional data structures are designed assuming thatrandom changes or random edits can be performed quickly and withoutpenalty. Flash, memory, however, has a penalty associated with smalledits. Small edits in a flash memory require the edited page to becopied forward to a new page. The previous page must be eventuallyerased before it can be reused. More specifically, data in a used areaor page of a flash memory cannot be simply overwritten in a conventionalflash memory. Rather, it is necessary to erase the page before writingthe data. This is the reason that small edits to a page in the flashmemory are simply written as a new page.

This process causes both a performance penalty and a lifespan penalty.This process results in multiple reads and writes (thus the performancepenalty). The lifespan penalty occurs because flash memory can only bewritten or erased a limited number of times before wearing out. Further,flash memory is typically erased in large units. Systems and methods areneeded to improve the performance of flash memory and to improve thelifespan of the flash memory.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which at least some aspects of thisdisclosure can be obtained, a more particular description will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only example embodiments of the invention and are not thereforeto be considered to be limiting of its scope, embodiments of theinvention will be described and explained with additional specificityand detail through the use of the accompanying drawings, in which:

FIG. 1 illustrates an example of a computing system that is configuredto perform overwrites in a flash memory;

FIG. 2 illustrates an example of a flash memory that is configured toperform overwrites;

FIG. 3 illustrates an example of internal logic for overwriting portionsof a flash memory; and

FIG. 4 illustrates an example of an external interface for overwritingportions of a flash memory and for locking portions of the flash memorywhen performing overwrites.

DETAILED DESCRIPTION OF SOME EXAMPLE EMBODIMENTS

Embodiments of the invention relate to systems and methods forprocessing large datasets. Embodiments of the invention further relateto systems and methods for processing large datasets in a flash memory(e.g., SSD (solid state drive)). Embodiments of the invention furtherrelate to systems and methods for controlling or managing flash memoryand to interfacing with flash memory.

In a conventional flash memory, the ability to set a bit (i.e., changefrom a logical 0 to a logical 1) may be supported. However, changing abit from a logical 1 to a logical 0 (unset the bit) is not supported atthis level (e.g., the bit level). Rather, it is necessary to erase alarger unit in the flash memory. By way of example, flash memory may beerased in 1 megabyte units. As a result, it is not generally possible tooverwrite existing data in flash. Instead, the data is written to a newlocation (which may have been previously erased) and the old location ismarked for erasure. Embodiments of the invention enable overwrites ofexisting data in some instances and in various data structures.Embodiments of the invention allow data structures to be implemented inflash while reducing the number of associated erasures by overwritingsome of the data.

A flash memory may include a controller and an interface (e.g., API(application programming interface)) associated with the flash memorycontroller. In one example, the logic of the flash memory controller isconfigured to perform writes to existing data (overwriting the existingdata) rather than write the data to a new location and mark the oldlocation for deletion. If necessary, the controller may cause the datato be simply written to a new location. For an overwrite operation, thecontroller may initially read the previous version of the page or blockbeing written. If the changes being written only result in the settingof more logical is (or changing 0s to 1s), then the existing page orblock can be overwritten. If some bits need to be unset (changed from 1sto 0s) in the flash memory, then the write may be performed normally toa new page. During this process (read-check-overwrite), the page orblock may be locked.

In another example, an overwrite can be achieved using calls to a flashmemory API. Calls include, by way of example, a logical-OR and aCompare-and-Swap.

During a logical-OR call, a client may provide a block of data and anaddress. The page (or pages depending on the size of the block of data)at that address is modified to the logical OR of its current contentswith the provided block. This only requires setting additional bits. Asa result, an overwrite may be performed on the current page or pageswithout the need to write to a new page or pages. The logical OR changes0s in the target block that correspond to 1s in the new data to be set.It may not be necessary to perform an OR operation for each bit in theoverwrite operation. It may only be necessary to identify the 0s thatneed to be changed to 1s.

An overwrite may occur in flash memory by performing a logical ORoperation. This operation ensures that 1s located in a target block areunaffected while 0s are potentially changed to 1s. The change occurswhen the data being overwritten to the target block contains a 1 wherethe target block contains a 0. A logical OR operation between bits A andB has the possible outcomes:

A B OR Result 0 0 0 0 1 1 1 0 1 1 1 1

A Compare-and-Swap call may be used for locking and threadsynchronization when performing overwrites. A client provides theprevious version of the block and the new version of the block. Morebits are set in the new version. The flash memory, in response to thecall, may atomically read the page and compare the read page/block withthe previous version provided by the client. If the previous versionprovided by the client matches the page read from the flash memory, thenthe page/block is overwritten with the new version provided by theclient in the call using, for example, a logical OR. Othercompare-and-swap operations to the same page are blocked until thecurrent call completes.

Embodiments of the invention further implement data structures in theflash memory such that the data structure can be updated usingoverwrites. This prolongs the life of the flash memory by limiting orreducing the number of erasures and can improve the performance of theflash memory. Examples of data structures include, but are not limitedto, bloom filters, linked lists, hash tables, locking data structures,trees, graphs, and the like or combinations thereof.

FIG. 1 illustrates an example of a computing system that includes aflash memory and that enables pages to be overwritten from an internalperspective and an external perspective. Overwrites to existing pages(without erasing the data first) can be achieved using internal logic.An external interface, which provides access to an API, allows similarabilities to be invoked by a client. As discussed herein, changing a bitfrom 0 to 1 is setting a bit and changing a bit from 1 to 0 is unsettinga bit. Unsetting bits can typically only be performed by erasing anerasure unit at a time and an erasure unit may include multiple pages.

FIG. 1 illustrates a computing system 100 that includes processors 102,DRAM 104, flash memory 106, and storage 114. The computing system 100may be configured to provide computing services such as backup services,document management, contact management, or the like. The computingsystem 100 can be formed of network connected devices or may beimplemented as an integrated unit. The computing system 100 can beconnected to a computing network.

The storage 114 may include various hardware storage devices (e.g.,magnetic, optical, etc.) such as HDDs. The storage 114 can be arrangedin different manners. The DRAM 104 and the flash 106 can be used ascaches in the computing system 100. The DRAM, which is the fastestmemory, is typically smaller than the flash memory 106. The flash memory106 is typically smaller than the storage 114. In other embodiments, theflash 106 may be the primary storage and the storage 114 could beomitted. The flash memory 106 can be large (e.g., terabytes or larger).The computing system 100 may be configured for processing large datasets such as backup data, data lake data, or the like.

The flash memory 106 is associated with a flash controller 108 and aflash API 110. The flash controller 108 typically controls operationsoccurring within the flash 106 and may include its own processor andmemory. The flash API 110 allows clients to make specific calls to theflash memory 106, which may be executed by the flash controller 108. Theclient may be any device or component (e.g., processor, memorycontroller, process) that interacts with the flash memory 106.

The flash controller 108 is associated with logic 112 that may beconfigured to interact with the data stored in the flash memory 106. Thelogic 112, for example, may perform overwrites, logical-ORs,compare-and-swaps, or the like.

FIG. 2 illustrates an example of a flash memory and illustrates how datamay be arranged in the flash memory. FIG. 2 illustrates a flash memory200, which is an example of the flash memory 106 shown in FIG. 1. Theflash memory 200 includes erasure units, such as erasure units 202 and212. Each erasure unit is associated with pages. Pages 204, 206, 208,and 210 are associated with the erasure unit 202 and the pages 214, 216,218, and 220 are associated with the erasure unit 212. One of skill inthe art can appreciate that the flash memory is typically much largerthan illustrated.

The pages 204, 206, 208, and 210 are smaller than the erasure unit 202.By way of example only, the pages 204, 206, 208, and 210 may be 4 KBeach. The erasure units 202 and 212 may be 1 MB each. Data stored in theflash memory 200 may also be arranged in containers or using otherstorage arrangements. However, when data is written to the flash memory200, the data is written in pages and the pages are usually written insequence.

In order to overwrite a page in a conventional flash, it is necessary toerase all pages in the erasure unit before writing the pages in thenewly erased erasure unit or write the new page to a new location. Forexample, the page 208 includes data. Because the page 208 contains data,a conventional flash cannot simply write new data to the page 208.Rather, it is necessary to erase all pages 204, 206, 208, and 210 in theerasure unit 202 before new data can be written to the page 208. Infact, all pages in the erasure unit 202 would be erased. The new datacould alternatively be written to a new location and the existing pageor erasure unit marked for erasure.

Embodiments of the invention, in contrast, allow data to be written tothe page 208 by performing an overwrite operation. In particular,embodiments of the invention allow data to be written to the page 208 orany other page in the erasure unit 202 as long as the write makes nochanges so specific cells (or bits) become unset, but only changes 0bits to 1s. This is because the flash memory 200 may allow moreelectrons to be stored in an individual cell (representing one bit) thussemantically changing the value from 0 to 1. Reducing the electrons tochange a 1 to a 0, however, involves erasing an entire erasure unit dueto the hardware constraints. Thus, data such as 0000 can be overwrittenas 0101 because only 0s are being changed to 1s. An overwrite is notpermitted when attempting to change 1110 to 0010 because this involveschanging 1s to 0s for this type of flash memory. In this case whenchanging 1s to 0s, it may be necessary to follow conventional flashmemory writing procedures, which may involve writing the data to a newpage and erasing the pages in the erasure unit.

FIG. 3 illustrates an example of a flash memory that includes acontroller and illustrates an example of logic associated withperforming an overwrite in the flash memory. FIG. 3 illustrates that theflash memory 300 may receive a write block 302 from a client (e.g., athread, process, or the like). When the write block 302 is received, thecontroller may perform controller logic 304 to perform the writeoperation in the flash memory 300.

The write operation may include performing a method 310. The write block302 may write to more than one page in the flash memory 300. In box 312,the controller 320 may read the target block 306. The target block 306may be, by way of example, a previous version of the write block 302.The target block 306 may be located at a destination address included inthe write request received along with the write block 302.

After reading the target block 306, the controller 320 may compare thetarget block 306 with the write block 302. The result of the comparisondetermines, in one example, whether the target block 306 can beoverwritten with the write block 302 or whether the write block iswritten to a new location as the new block 308. The comparison mayidentify which bits need to be changed from 0s to 1s.

In one example, if the comparison in box 314 determines that writing thewrite block 302 to the target block 306 would only set bits from 0 to 1,then the target block 306 is overwritten with the write block 302 in box316. If the comparison determines that it is necessary to reset 1s to0s, then the write block 302 is written to a new location as the newblock 308 in box 318. The target block 306 may be marked for deletion orerasure.

The logic performed in the method 310 is internal to the flash memory300 in this example. The client associated with the write operation maynot be aware of the overwrite method performed in the flash memory 300.

During the method 310 and in particular while reading the target block,comparing the target block with the write block and overwriting thetarget block, the page or pages associated with the target block arelocked at 320 so that another client does not interfere with the method310. A lock may be used during the overwrite method 310. The controller320 may set aside some memory to track which regions of the flash memory300 are locked.

FIG. 4 illustrates an example of an external interface for overwrites ina flash memory. FIG. 4 illustrates a flash memory 400, which is anexample of the flash memory 106 in FIG. 1. The flash memory 400 includesa controller 406 and an API 408. The API 408 includes calls 410including, by way of example, a logical-OR 412 and a Compare and Swap414.

In contrast to the internal logic illustrated in FIG. 3, the API allowsa client to explicitly call the API 408. The logical-OR call 412 allowsa client 402 to provide a block of data and an address 404. A logical ORis performed between the page or pages at the address provided in theclient request 402 with the block 416 at the specified address. Thiscall compares or performs a logical OR with each respective bit. Alogical OR has the property that it never changes a one to a zero, butzeros may be changed to one if they are ORed with a one. This operationis an overwrite that potentially replaces 0s in the block 416 to 1s. Theclient may be aware, prior to making the call, that the necessaryupdates to the block 416 can be achieved with the logical OR operation.Depending on hardware capabilities, a logical OR operation may not berequired for each bit. Rather, the logical OR effectively changes 0s into the block 416 to 1s based on the contents of the block provided inthe client request 402. Thus, the logical OR may simply identify thebits to be changed to 1s and make those changes. If the hardware isconfigures such that an entire page is written at a time, then the pageis written such that the relevant 0s are changed to 1s.

The compare and swap call 414 can be used for locking and for threadsynchronization when performing overwrites. When making a compare andswap call 414, the client may provide a previous version of a block anda new version of the block. The new version may have new bits set. Thecontroller 406 may then compare the previous version included in therequest with the block 416 to insure that another client has not changedthe block. If the comparison is equal, the block 416 can be overwritten(e.g., by using logical-OR operation) with the new version included inthe client request 402. Other callers attempting to impact or alterblock 416 will be blocked until these compare and swap operationcompletes. Thus, the controller 406 may also lock locations in the flashmemory 400 that are being updated or changed in accordance with thecontroller logic or API calls 410.

The calls and logic discussed herein may be implemented with computerexecutable instructions and the controller 406 and/or the flash memory400 are examples of a computing device. The calls and logic discussedherein may also be used when interacting (e.g., read/write/update) withdata structures implemented in a flash memory.

The embodiments disclosed herein may include the use of a specialpurpose or general-purpose computer including various computer hardwareor software modules, as discussed in greater detail below. A computermay include a processor and computer storage media carrying instructionsthat, when executed by the processor and/or caused to be executed by theprocessor, perform any one or more of the methods disclosed herein.

As indicated above, embodiments within the scope of the presentinvention also include computer storage media, which are physical mediafor carrying or having computer-executable instructions or datastructures stored thereon. Such computer storage media can be anyavailable physical media that can be accessed by a general purpose orspecial purpose computer.

By way of example, and not limitation, such computer storage media cancomprise hardware such as solid state disk (SSD), RAM, ROM, EEPROM,CD-ROM, flash memory, DRAM, phase-change memory (“PCM”), or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other hardware storage devices which can be used tostore program code in the form of computer-executable instructions ordata structures, which can be accessed and executed by a general-purposeor special-purpose computer system to implement the disclosedfunctionality of the invention. Combinations of the above should also beincluded within the scope of computer storage media. Such media are alsoexamples of non-transitory storage media, and non-transitory storagemedia also embraces cloud-based storage systems and structures, althoughthe scope of the invention is not limited to these examples ofnon-transitory storage media.

Computer-executable instructions comprise, for example, instructions anddata which cause a general purpose computer, special purpose computer,or special purpose processing device to perform a certain function orgroup of functions. Although the subject matter has been described inlanguage specific to structural features and/or methodological acts, itis to be understood that the subject matter defined in the appendedclaims is not necessarily limited to the specific features or actsdescribed above. Rather, the specific features and acts disclosed hereinare disclosed as example forms of implementing the claims.

As used herein, the term ‘module’ or ‘component’ can refer to softwareobjects or routines that execute on the computing system. The differentcomponents, modules, engines, and services described herein may beimplemented as objects or processes that execute on the computingsystem, for example, as separate threads. While the system and methodsdescribed herein can be implemented in software, implementations inhardware or a combination of software and hardware are also possible andcontemplated. In the present disclosure, a ‘computing entity’ may be anycomputing system as previously defined herein, or any module orcombination of modules running on a computing system.

In at least some instances, a hardware processor is provided that isoperable to carry out executable instructions for performing a method orprocess, such as the methods and processes disclosed herein. Thehardware processor may or may not comprise an element of other hardware,such as the computing devices and systems disclosed herein. A controllermay include a processor and memory and/or other computing chips.

In terms of computing environments, embodiments of the invention can beperformed in client-server environments, whether network or localenvironments, or in any other suitable environment. Suitable operatingenvironments for at least some embodiments of the invention includecloud computing environments where one or more of a client, server, ortarget virtual machine may reside and operate in a cloud environment.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed is:
 1. In a system that includes a flash memory, amethod for writing data to the flash memory, the method comprising:receiving a call from a client to write data to a location in the flashmemory, wherein the client specifies in the call how to write the data;determining whether the location can be overwritten; overwriting thelocation when the location can be overwritten, wherein the location isoverwritten in a manner specified in the call; and marking the locationfor erasure when the location cannot be overwritten.